US 3794159 A
Process for flotation of large size mineral particles which comprises mixing the turbid liquid which is to be subjected to flotation with a fine particle size weighting agent by which the large size particles are made more buoyant and are on treatment with air bubbles more easily floated out.
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Description (OCR text may contain errors)
United States Patent 1191 1 Singewald 1 Feb. 26, 1974 1 PROCESS FOR FLOTATION 0F LARGE 2,340,613 2 1944 Perkins 209 166 SIZE MINERAL PARTICLES 2,696,299 12/1954 2,756,965 7/1956  Inventor: Arno Smgewald, Kassel, Germany 2 990 95 7 9 3,425,546 2/1969  Ass'gnee' wmtershaAkt'engeseuschafl 2965 446 12 1960 Cramer 209/173 x Kasselicermany 2,650,706 9/1953 Colin 209/173 1 1 i 1970 FOREIGN PATENTS OR APPL1CAT1ONS  Appl. N6; 98,210 144,482 12 1951 Austria 209 173 1,138,350 1/1957 France 209/166 52 US. Cl 209/12, 209/166, 209/173 Primary Examine, RObert Halper  Int. Cl B03b 7/00 A A t F M' h s St 58 Field 61 Search 209/166,'167, 164, 172, 172.5, gen ae n r 209/1731 12 57 ABSTRACT [59 iizzz ioizgrizz iifiing 112 1111; 13112 23117135: UNITED STATES PATENTS be subjected to flotation with a fine particle size HOCI'H X agent the large ize parti lc are 2 3 at made more buoyant and are on treatment with air e ron 2,110,760 3/1938 DeVuuys 209 1725 bubbles more edslly floated 2,139,047 12/1938 Fromp 209/1725 7 Claims, N0 Drawings This invention relates to a process for separating large size mineral particles from liquors containing the same, said process constituting a combined gravity and flotation separation.
In the conventional foam flotation processes, the amount of particles separated is always limited by the fact that the too heavy particles cannot be floated out by treatment with air bubbles as the amount of air bubbles which can be provided in relationship to the weight of the particles is not adequate for making the agglomerates of particles and bubbles lighter than the liquid.
For this reason, various processes have been proposed whereby the amount of air bubbles generated can be increased. These include the use of auxiliary agents, as for instance fuel oil in admixture with foaming agents, the same constituting a source of supply of additional foam. However, very often the relatively large bubbles thus provided are not in a condition in which they can adhere to the correspondingly large size particles. It has therefore been attempted through the evolution of dissolved gases in the liquors to form of the air bubbles thus evolved nuclei to which larger bubbles will adhere thereby forming still larger bubbles.
It has also already been proposed that the separation of the large size particles be improved by the use of correspondingly larger flotation cells, that is through the use of special air supplying equipment or by providing for a sinking down of the particles against a counter directed upwardly flowing flotation carrier liquor.
Still further, it has been proposed to use in place of pure water as the flotation carrier liquor, aqueous salt solutions which have a correspondingly high'specific weight. However, very often, such dissolved salts adversely influence the effectiveness of the flotation reagents. Thus, for example, it is known that salt solutions are entirely ineffective to bring about a flotation of the large size particles in a sylvite flotation.
In accordance with the invention, it has been'foun'd that particular advantages are realized if in the flotation of the larger particles, the flotation liquor is treated with a weighting agent so that the heavy particles lose a part of their weight by the apparent specific gravity increase of the flotation liquor and .then can be easily removed possibly after adding conventional collection agents, by introduction of the air bubbles.
This process is of particular importance in carrying out separations of heavy mixtures as for instance, the separation of the heavy mineral materials accumulated in operating sieve or jig machines or which have been recovered from cyclone separating procedures. The separation of such mixtures introduces many problems, particularly in connection with the apparatus required. Such particles as are here involved, are for instance those too heavy to be separated in cyclones, or for instance those particles having a size of over 1 mm and also those particles which are too fine to be classified by the conventional industrial machines, for instance those particles having a size under 5 mm. Basically, difficulties arise with respect to a gravity separation when the specific weights of the different particles to be separated are very close to each other, i.e., all under 0.2 g/cm difference from each other (in the case of KCl 1.99 g/cm NaCl 2.17 g/cm"). Such a separation is particularly difficult when for example such particles are to be separated into three grades, i.e., a low and high specific weight fraction and also a medium weight fraction.
The applicant provides for the first time a method where such difficult separations can be carried out simply and reliably, the method combining into a single process a flotation separation and a gravity separation.
Thus in accordance with the invention there is provided a process for separating large size mineral particles which comprises mixing the turbid liquid prior to its being subjected to flotation with a fine particle size weighting agent whereby the large size particles are made more buoyant and then subjecting the flotation mixture to treatment with air bubbles the particles thereafter being more easily floated out.
In accordance with the invention, as the weighting agent for the gravimetric working up of the particles, there are suitable for use those substances which in carrying out the known purely gravity separations impart stability to the quasi difficulty separable liquors and are used therein in an extremely finely divided form. In this connection flotation separations have been carried out prior to the invention under addition of finely ground ferrosilicon or magnetite. There has very often resulted that when air bubbles are introduced into such a mixture, the bubbles similarly, as in the case with troublesome. sludge formers, are coated over with the finely divided weighting agents so that they are no longer able to adhere to the heavy mineral particles and bring about their flotation. It has accordingly now been established that as weighting agents for larger size particles there must be used only those particles which in flotation processes are generally known to inhibit bubble formation in the sludge. Thus in accordance with the invention the particles of weighting agent are required to have a size larger than 0.06 0.1 but they must not be so large that they cannot be satisfactorily dispersed in the flotation cell and for these purposes are preferably not larger than 1.0 mm.
In carrying out flotation separations as herein taught, it was sought to avoid the disadvantages arising from the use of fine particle size weighting agents (between 0.06 1.0 mm) by additionally introducing a conventional collection agent. However this had the disadvantageous effect that the fine particles were rapidly floated out during the flotation of the larger particles so that further additions of both the fine particles and collecting agent were necessitated. It has been established that it is only by the specific combination of a gravity separation with a flotation that the process is made feasible and that it is only through the use as weighting agents of those substances which in the flotation do not-have properties whereby they are adsorbed by the collecting agents and also whereby the weighting agents do not specifically adhere to the air bubbles that the separation can be satisfactorily carried out. It is to be understood that there cannot be avoided, or only to a slight degree, that the fine particle weighting agents due to turbulence and strong air currents in the flotation liquor are floated out together with the foam in the resultant concentrate. In this event, the weighting agent fine particles can thereafter be easily separated from the heavy large size mineral particles.
The Examples which follow were carried out with large particle size sylvite (KCl), the separation being carried out with alkylamines, the sylvite particles being separated from their naturally accompanying mineral substances. The separation by flotation of such soluble materials, here KCl, is conventionally carried out from saturated solutions. Such solutions already have a specific weight of 1.2 1.3 g/cm so that it is necessary to provide a high buoying force to effect the desired separation similar to the situation where insoluble substances are to be floated out of water.
Heretofore, the necessary increase in specific weight of the carrier liquid as is required to bring about a satisfactory recovery of heavy sylvite has not been obtainable. As a result, there have been used such reagent combinations as large amounts of alkylamine hydrochloride plus fuel oil plus foam. In carrying out the following Examples, there were used in one series of experiments 100 g/ton of a mixture of fuel oil and float oil. The flotation yields even with such additions did not prove satisfactory and it was only when the process of the invention was followed that an essential increase in the yield of the large particles was realized. This only occurred when the specific weight of the carrier liquid was increased through the addition of weighting agents to a value of about 1.6 g/cc. There then resulted that in the resultant quasi-heavy liquid, the large particles undergo a considerable weight loss so that their foam flotation is made easier.
The weight of the turbid liquid containing the particles to be separated amounts in the Examples to 1.6 g/cm and is brought about by an addition of 0.77t of the weighting agent, in this case finely divided rock salt, to l m of turbid liquid.
EXAMPLES A. Coarse grained sylvite having a purity of more than 80 percent) fraction 2.0 3 mm.
1. Flotation in NaCl/KCl solution (p= 1.25) KCl difficult to bring to flotation, with 1,200 g/t aminohydrochloride only 38.5 percent of the sylvite (present as a 61 percent K 0 concentrate) is brought to flotation.
2. In a weighted NaCl/KCl solution (p 1.6) with 400 g/t 85.0 percent of the sylvite (present as a 61.7 percent K 0 concentrate) is already brought to flotation.
The aeration in the flotation cell is very carefully carried out so that only 4.6 percent of the weighting agent is carried off with the concentrate. The following fractions are recovered following classification from the concentrate and the residue:
Sieve Concen- Analysis trate Residue Concentrate Residue 00.5mm 15.4 1.6 1.2 2.1
1.0-1.5mm 43.7 8.2 10.8 9.6 1.5-2 0mm 17.3 27.6 13.9 14.5
Sieve Concern Analysis trate Residue Concentrate Residue 0-(1.5mm 30.8 4.4 2.6 0.5-1.0mm 12.5 3.4 8.4 6.7
l0-l.5mm 19.2 6.7 14.8 12.3 1 52.0mm 17.5 11.6 19.2 17.1 2 02.5mm 14.2 35.9 32.8 36.0 2 53.0mm 5.8 38.0 22.0 25.3
Frequently by the use of the weighting agent, the particle destruction normally taking place in the flotation cell is checked.
C. A heavy washed out medium fine fraction is reduced in size and a 2.0 4.0 mm screened KCl- NaCl mineral mixture with 25.2 percent K 0 having the following particle distribution brought to flotation:
'1. Using 500 g/t aminohydrochloride in an 'unweighted carrier liquor, 56.4 percent of the floated KCl (56.0 percent K 0 purity) was recovered as a concentrate.
2. Using only g/t aminohydrochloride in 1 a weighted liquor, 82.9 percent of the charged KCl (having a 59.6 percent K 0 purity) were floated out.
Thereafter using powerful aeration, 84.0 percent of the weighting agent was recovered with the concentrate and by screening those particles having a size of up to 0.3 mm further separated out.
D. In a similar manner, products in the 3.0 4.0 mm fraction were separated out by flotation in an unweighted sludge, a 36.8 percent yield was obtained, as
compared to a 73.8 percent yield recovered using a weighted sludge (turbid liquor) in accordance with the invention.
In an analogous manner, the flotation of other minerals can be carried out with different weighting agents, as for instance, the flotation of kieserite in carrier 1iquors in admixture with rock salt, of kieserite in water through the use of insoluble weighting agents. In reverse rock salt/KC] separations can be carried out through flotation of the rock salt, for instance with condensation products of fatty acids and urea as described in DBB No. 1,191,764, fine particle kieserite being used as the weighting agent, and heavy NaC l thereby floated out. In this case also, there is no need to use only the conventional weighting agents.
In summary, flotation in salt liquors is preferably carried out using salts and insoluble materials, the flotation in water is preferably carried out with insoluble agents, the conventional weighting agents such as ferrosilicon, magnetite and the like preferably being used in this connection.
The weighting agents following completion of the flotation can or cannot be recovered. Inasmuch as a part of the weighting agent has been more or less been foamed off with the concentrate, the large sized particles and the fine sized weighting agent can be separated with particle size classifying apparatus such as sieves, screeners, etc. It is also possible for the weighting agent to be separated from the residue through electric or electrostatic separation processes based on the different properties of the large particles as compared to those of the fine particles. It is further possible that after the flotation of the heavy material, the weighting agent can be easily separated by floating out the same from the concentrate and from the residue if there are introduced following the fine particle weighting agent suitable collecting agents. Where an insoluble or difficulty soluble large particle substance is to be floated out from a salt liquor, and there is used as weighting agent a fine particle salt, then the latter can be recovered from the concentrate or residue by dissolution with water.
It is also possible to use as weighting agent, finely ground and preferably classified residues and even such fine particle materials as cannot be selectively separated out by means of the conventional collection agents.
The process of the invention directed at flotation separation of large size particles fills the gaps existing between the pure flotation and pure heavy liquid separation processes and is particularly adaptable for use in connection with mineral particles having a size of from 1 5 mm and having low specific weights and is also suitable in connection with mineral particles having higher specific weights but having a particle size of about 0.1 mm.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. I
What is claimed as new and desired to be protected by Letters Patent is:
l. A process for the flotation of large grain size mineral particles having a size from above 1 and up to 5 mm comprising forming an aqueous flotation suspension in which suspension a collection agent is present and, additionally introducing a weighting agent in the form of fine grain particles into the suspension of a size from above 0.06 and up to 1 mm, said fine grain agent particles being chemically different from said large grain particles, being non-adherent to said collection agent-and to airbubbles, so as to increase the density of the suspension, and then carrying out the flotation of the thus buoyed large-grain mineral particles by means of aeration to form air bubbles in said suspension.
2. The process of claim 1, where aeration of the suspension is effected to an extent limited to that which causes only a minor amount of said fine-grain particles to be recovered with the float concentrate resulting from said flotation.
3. The process of claim 1, wherein the fine-grain particles are finely divided rock salt.
4. The process of claim 1, wherein the large-grain particles are sylvite which particles are present in said suspension as a saturated solution and wherein the specific weight of said solution is increased from between about 1.2 and 1.3 to about 1.6 g/cc by additionof said fine grain particles.
5. The process of claim 4, wherein the fine-grain particles are rock salt.
6. The process of claim 1, wherein the flotation is carried out in a salt liquor and the fine-grain particles are of a material insoluble therein so as to facilitate subsequent separation of said solid fine-grain particles from said salt liquor.
7. The process of claim 1, wherein the large-grain particles and fine-grain particles if present together either in the concentrate or in the residue of the flotation are subsequently separated by screening, an electrostatic operation or a second flotation operation.